MapGenerator only calls mapping function if the result is used

Previously the mapping was eager on construction and calls to
`next()`. This was fine when generators were always exhausted fully,
but with the new generator filtering, we might not want to call
the map function eagerly; rather we want to call it only once,
after the generator is moved to the target element.

13 files changed, 83 insertions, 52 deletions

diff --git a/src/catch2/generators/catch_generators_adapters.hpp b/src/catch2/generators/catch_generators_adapters.hpp
index 2f6d8ed3..c46cb927 100644
--- a/src/catch2/generators/catch_generators_adapters.hpp
+++ b/src/catch2/generators/catch_generators_adapters.hpp
@@ -11,6 +11,7 @@
 #include <catch2/generators/catch_generators.hpp>
 #include <catch2/internal/catch_meta.hpp>
 #include <catch2/internal/catch_move_and_forward.hpp>
+#include <catch2/internal/catch_optional.hpp>
 
 #include <cassert>
 
@@ -182,7 +183,7 @@ namespace Generators {
         GeneratorWrapper<U> m_generator;
         Func m_function;
         // To avoid returning dangling reference, we have to save the values
-        T m_cache;
+        mutable Optional<T> m_cache;
 
         void skipToNthElementImpl( std::size_t n ) override {
             for ( size_t curr = GeneratorUntypedBase::currentElementIndex();
@@ -202,19 +203,16 @@ namespace Generators {
         template <typename F2 = Func>
         MapGenerator(F2&& function, GeneratorWrapper<U>&& generator) :
             m_generator(CATCH_MOVE(generator)),
-            m_function(CATCH_FORWARD(function)),
-            m_cache(m_function(m_generator.get()))
+            m_function(CATCH_FORWARD(function))
         {}
 
         T const& get() const override {
-            return m_cache;
+            if ( !m_cache ) { m_cache = m_function( m_generator.get() ); }
+            return *m_cache;
         }
         bool next() override {
-            const auto success = m_generator.next();
-            if (success) {
-                m_cache = m_function(m_generator.get());
-            }
-            return success;
+            m_cache.reset();
+            return m_generator.next();
         }
 
         bool isFinite() const override { return m_generator.isFinite(); }
diff --git a/tests/SelfTest/Baselines/compact.sw.approved.txt b/tests/SelfTest/Baselines/compact.sw.approved.txt
index a7677dcd..61328ce6 100644
--- a/tests/SelfTest/Baselines/compact.sw.approved.txt
+++ b/tests/SelfTest/Baselines/compact.sw.approved.txt
@@ -1259,14 +1259,15 @@ Approx.tests.cpp:<line number>: passed: d <= Approx( 1.22 ).epsilon(0.1) for: 1.
 <=
 Approx( 1.21999999999999997 )
 Misc.tests.cpp:<line number>: passed: with 1 message: 'was called'
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == 0 for: 0 == 0
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 4 for: 4 == 4
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 2 == 2
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 1 == 1
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 4 for: 4 == 4
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 2 == 2
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 1 == 1
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 6 for: 6 == 6
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 3 == 3
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 2 == 2
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.skipToNthElement( 7 )
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 3 == 3
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 2 == 2
 Matchers.tests.cpp:<line number>: passed: testStringForMatching(), ContainsSubstring( "string" ) && ContainsSubstring( "abc" ) && ContainsSubstring( "substring" ) && ContainsSubstring( "contains" ) for: "this string contains 'abc' as a substring" ( contains: "string" and contains: "abc" and contains: "substring" and contains: "contains" )
 Matchers.tests.cpp:<line number>: passed: testStringForMatching(), ContainsSubstring( "string" ) || ContainsSubstring( "different" ) || ContainsSubstring( "random" ) for: "this string contains 'abc' as a substring" ( contains: "string" or contains: "different" or contains: "random" )
 Matchers.tests.cpp:<line number>: passed: testStringForMatching2(), ContainsSubstring( "string" ) || ContainsSubstring( "different" ) || ContainsSubstring( "random" ) for: "some completely different text that contains one common word" ( contains: "string" or contains: "different" or contains: "random" )
@@ -2984,6 +2985,6 @@ InternalBenchmark.tests.cpp:<line number>: passed: q3 == 23. for: 23.0 == 23.0
 Misc.tests.cpp:<line number>: passed:
 Misc.tests.cpp:<line number>: passed:
 test cases:  449 |  329 passed |  96 failed | 6 skipped | 18 failed as expected
-assertions: 2399 | 2198 passed | 158 failed | 43 failed as expected
+assertions: 2400 | 2199 passed | 158 failed | 43 failed as expected
 
 
diff --git a/tests/SelfTest/Baselines/compact.sw.multi.approved.txt b/tests/SelfTest/Baselines/compact.sw.multi.approved.txt
index 65146fc5..4b32eb63 100644
--- a/tests/SelfTest/Baselines/compact.sw.multi.approved.txt
+++ b/tests/SelfTest/Baselines/compact.sw.multi.approved.txt
@@ -1257,14 +1257,15 @@ Approx.tests.cpp:<line number>: passed: d <= Approx( 1.22 ).epsilon(0.1) for: 1.
 <=
 Approx( 1.21999999999999997 )
 Misc.tests.cpp:<line number>: passed: with 1 message: 'was called'
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == 0 for: 0 == 0
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 4 for: 4 == 4
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 2 == 2
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 1 == 1
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 4 for: 4 == 4
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 2 == 2
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_1 + 1 for: 1 == 1
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.get() == 6 for: 6 == 6
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 3 == 3
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 2 == 2
 GeneratorsImpl.tests.cpp:<line number>: passed: map_generator.skipToNthElement( 7 )
-GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 3 == 3
+GeneratorsImpl.tests.cpp:<line number>: passed: map_calls == map_calls_2 + 1 for: 2 == 2
 Matchers.tests.cpp:<line number>: passed: testStringForMatching(), ContainsSubstring( "string" ) && ContainsSubstring( "abc" ) && ContainsSubstring( "substring" ) && ContainsSubstring( "contains" ) for: "this string contains 'abc' as a substring" ( contains: "string" and contains: "abc" and contains: "substring" and contains: "contains" )
 Matchers.tests.cpp:<line number>: passed: testStringForMatching(), ContainsSubstring( "string" ) || ContainsSubstring( "different" ) || ContainsSubstring( "random" ) for: "this string contains 'abc' as a substring" ( contains: "string" or contains: "different" or contains: "random" )
 Matchers.tests.cpp:<line number>: passed: testStringForMatching2(), ContainsSubstring( "string" ) || ContainsSubstring( "different" ) || ContainsSubstring( "random" ) for: "some completely different text that contains one common word" ( contains: "string" or contains: "different" or contains: "random" )
@@ -2973,6 +2974,6 @@ InternalBenchmark.tests.cpp:<line number>: passed: q3 == 23. for: 23.0 == 23.0
 Misc.tests.cpp:<line number>: passed:
 Misc.tests.cpp:<line number>: passed:
 test cases:  449 |  329 passed |  96 failed | 6 skipped | 18 failed as expected
-assertions: 2399 | 2198 passed | 158 failed | 43 failed as expected
+assertions: 2400 | 2199 passed | 158 failed | 43 failed as expected
 
 
diff --git a/tests/SelfTest/Baselines/console.std.approved.txt b/tests/SelfTest/Baselines/console.std.approved.txt
index 7e9a3cdc..7773dea3 100644
--- a/tests/SelfTest/Baselines/console.std.approved.txt
+++ b/tests/SelfTest/Baselines/console.std.approved.txt
@@ -1744,5 +1744,5 @@ due to unexpected exception with message:
 
 ===============================================================================
 test cases:  449 |  347 passed |  76 failed | 7 skipped | 19 failed as expected
-assertions: 2377 | 2198 passed | 136 failed | 43 failed as expected
+assertions: 2378 | 2199 passed | 136 failed | 43 failed as expected
 
diff --git a/tests/SelfTest/Baselines/console.sw.approved.txt b/tests/SelfTest/Baselines/console.sw.approved.txt
index 71a38625..de8be563 100644
--- a/tests/SelfTest/Baselines/console.sw.approved.txt
+++ b/tests/SelfTest/Baselines/console.sw.approved.txt
@@ -8260,6 +8260,11 @@ GeneratorsImpl.tests.cpp:<line number>
 ...............................................................................
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
+  REQUIRE( map_calls == 0 )
+with expansion:
+  0 == 0
+
+GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 4 )
 with expansion:
   4 == 4
@@ -8267,7 +8272,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_1 + 1 )
 with expansion:
-  2 == 2
+  1 == 1
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 4 )
@@ -8277,7 +8282,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_1 + 1 )
 with expansion:
-  2 == 2
+  1 == 1
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 6 )
@@ -8287,7 +8292,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_2 + 1 )
 with expansion:
-  3 == 3
+  2 == 2
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE_THROWS( map_generator.skipToNthElement( 7 ) )
@@ -8295,7 +8300,7 @@ GeneratorsImpl.tests.cpp:<line number>: PASSED:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_2 + 1 )
 with expansion:
-  3 == 3
+  2 == 2
 
 -------------------------------------------------------------------------------
 Matchers can be (AllOf) composed with the && operator
@@ -20030,5 +20035,5 @@ Misc.tests.cpp:<line number>: PASSED:
 
 ===============================================================================
 test cases:  449 |  329 passed |  96 failed | 6 skipped | 18 failed as expected
-assertions: 2399 | 2198 passed | 158 failed | 43 failed as expected
+assertions: 2400 | 2199 passed | 158 failed | 43 failed as expected
 
diff --git a/tests/SelfTest/Baselines/console.sw.multi.approved.txt b/tests/SelfTest/Baselines/console.sw.multi.approved.txt
index 26723baa..0598bd09 100644
--- a/tests/SelfTest/Baselines/console.sw.multi.approved.txt
+++ b/tests/SelfTest/Baselines/console.sw.multi.approved.txt
@@ -8258,6 +8258,11 @@ GeneratorsImpl.tests.cpp:<line number>
 ...............................................................................
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
+  REQUIRE( map_calls == 0 )
+with expansion:
+  0 == 0
+
+GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 4 )
 with expansion:
   4 == 4
@@ -8265,7 +8270,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_1 + 1 )
 with expansion:
-  2 == 2
+  1 == 1
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 4 )
@@ -8275,7 +8280,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_1 + 1 )
 with expansion:
-  2 == 2
+  1 == 1
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_generator.get() == 6 )
@@ -8285,7 +8290,7 @@ with expansion:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_2 + 1 )
 with expansion:
-  3 == 3
+  2 == 2
 
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE_THROWS( map_generator.skipToNthElement( 7 ) )
@@ -8293,7 +8298,7 @@ GeneratorsImpl.tests.cpp:<line number>: PASSED:
 GeneratorsImpl.tests.cpp:<line number>: PASSED:
   REQUIRE( map_calls == map_calls_2 + 1 )
 with expansion:
-  3 == 3
+  2 == 2
 
 -------------------------------------------------------------------------------
 Matchers can be (AllOf) composed with the && operator
@@ -20019,5 +20024,5 @@ Misc.tests.cpp:<line number>: PASSED:
 
 ===============================================================================
 test cases:  449 |  329 passed |  96 failed | 6 skipped | 18 failed as expected
-assertions: 2399 | 2198 passed | 158 failed | 43 failed as expected
+assertions: 2400 | 2199 passed | 158 failed | 43 failed as expected
 
diff --git a/tests/SelfTest/Baselines/junit.sw.approved.txt b/tests/SelfTest/Baselines/junit.sw.approved.txt
index efcd49cf..3f302f98 100644
--- a/tests/SelfTest/Baselines/junit.sw.approved.txt
+++ b/tests/SelfTest/Baselines/junit.sw.approved.txt
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="141" skipped="12" tests="2411" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="141" skipped="12" tests="2412" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <properties>
       <property name="random-seed" value="1"/>
       <property name="filters" value="&quot;*&quot; ~[!nonportable] ~[!benchmark] ~[approvals]"/>
diff --git a/tests/SelfTest/Baselines/junit.sw.multi.approved.txt b/tests/SelfTest/Baselines/junit.sw.multi.approved.txt
index e59f9e92..e624506c 100644
--- a/tests/SelfTest/Baselines/junit.sw.multi.approved.txt
+++ b/tests/SelfTest/Baselines/junit.sw.multi.approved.txt
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuites>
-  <testsuite name="<exe-name>" errors="17" failures="141" skipped="12" tests="2411" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="141" skipped="12" tests="2412" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <properties>
       <property name="random-seed" value="1"/>
       <property name="filters" value="&quot;*&quot; ~[!nonportable] ~[!benchmark] ~[approvals]"/>
diff --git a/tests/SelfTest/Baselines/tap.sw.approved.txt b/tests/SelfTest/Baselines/tap.sw.approved.txt
index 1909b8f6..e5f640e2 100644
--- a/tests/SelfTest/Baselines/tap.sw.approved.txt
+++ b/tests/SelfTest/Baselines/tap.sw.approved.txt
@@ -2061,21 +2061,23 @@ ok {test-number} - d <= Approx( 1.22 ).epsilon(0.1) for: 1.22999999999999998 <=
 # ManuallyRegistered
 ok {test-number} - with 1 message: 'was called'
 # MapGenerator can be skipped forward efficiently
+ok {test-number} - map_calls == 0 for: 0 == 0
+# MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 4 for: 4 == 4
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_1 + 1 for: 2 == 2
+ok {test-number} - map_calls == map_calls_1 + 1 for: 1 == 1
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 4 for: 4 == 4
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_1 + 1 for: 2 == 2
+ok {test-number} - map_calls == map_calls_1 + 1 for: 1 == 1
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 6 for: 6 == 6
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_2 + 1 for: 3 == 3
+ok {test-number} - map_calls == map_calls_2 + 1 for: 2 == 2
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.skipToNthElement( 7 )
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_2 + 1 for: 3 == 3
+ok {test-number} - map_calls == map_calls_2 + 1 for: 2 == 2
 # Matchers can be (AllOf) composed with the && operator
 ok {test-number} - testStringForMatching(), ContainsSubstring( "string" ) && ContainsSubstring( "abc" ) && ContainsSubstring( "substring" ) && ContainsSubstring( "contains" ) for: "this string contains 'abc' as a substring" ( contains: "string" and contains: "abc" and contains: "substring" and contains: "contains" )
 # Matchers can be (AnyOf) composed with the || operator
@@ -4817,5 +4819,5 @@ ok {test-number} - q3 == 23. for: 23.0 == 23.0
 ok {test-number} -
 # xmlentitycheck
 ok {test-number} -
-1..2411
+1..2412
 
diff --git a/tests/SelfTest/Baselines/tap.sw.multi.approved.txt b/tests/SelfTest/Baselines/tap.sw.multi.approved.txt
index 8c765346..4e64b316 100644
--- a/tests/SelfTest/Baselines/tap.sw.multi.approved.txt
+++ b/tests/SelfTest/Baselines/tap.sw.multi.approved.txt
@@ -2059,21 +2059,23 @@ ok {test-number} - d <= Approx( 1.22 ).epsilon(0.1) for: 1.22999999999999998 <=
 # ManuallyRegistered
 ok {test-number} - with 1 message: 'was called'
 # MapGenerator can be skipped forward efficiently
+ok {test-number} - map_calls == 0 for: 0 == 0
+# MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 4 for: 4 == 4
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_1 + 1 for: 2 == 2
+ok {test-number} - map_calls == map_calls_1 + 1 for: 1 == 1
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 4 for: 4 == 4
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_1 + 1 for: 2 == 2
+ok {test-number} - map_calls == map_calls_1 + 1 for: 1 == 1
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.get() == 6 for: 6 == 6
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_2 + 1 for: 3 == 3
+ok {test-number} - map_calls == map_calls_2 + 1 for: 2 == 2
 # MapGenerator can be skipped forward efficiently
 ok {test-number} - map_generator.skipToNthElement( 7 )
 # MapGenerator can be skipped forward efficiently
-ok {test-number} - map_calls == map_calls_2 + 1 for: 3 == 3
+ok {test-number} - map_calls == map_calls_2 + 1 for: 2 == 2
 # Matchers can be (AllOf) composed with the && operator
 ok {test-number} - testStringForMatching(), ContainsSubstring( "string" ) && ContainsSubstring( "abc" ) && ContainsSubstring( "substring" ) && ContainsSubstring( "contains" ) for: "this string contains 'abc' as a substring" ( contains: "string" and contains: "abc" and contains: "substring" and contains: "contains" )
 # Matchers can be (AnyOf) composed with the || operator
@@ -4806,5 +4808,5 @@ ok {test-number} - q3 == 23. for: 23.0 == 23.0
 ok {test-number} -
 # xmlentitycheck
 ok {test-number} -
-1..2411
+1..2412
 
diff --git a/tests/SelfTest/Baselines/xml.sw.approved.txt b/tests/SelfTest/Baselines/xml.sw.approved.txt
index 92852769..f104f74b 100644
--- a/tests/SelfTest/Baselines/xml.sw.approved.txt
+++ b/tests/SelfTest/Baselines/xml.sw.approved.txt
@@ -9927,6 +9927,14 @@ Approx( 1.21999999999999997 )
   <TestCase name="MapGenerator can be skipped forward efficiently" tags="[generators][map]" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
       <Original>
+        map_calls == 0
+      </Original>
+      <Expanded>
+        0 == 0
+      </Expanded>
+    </Expression>
+    <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
+      <Original>
         map_generator.get() == 4
       </Original>
       <Expanded>
@@ -9938,7 +9946,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_1 + 1
       </Original>
       <Expanded>
-        2 == 2
+        1 == 1
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9954,7 +9962,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_1 + 1
       </Original>
       <Expanded>
-        2 == 2
+        1 == 1
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9970,7 +9978,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_2 + 1
       </Original>
       <Expanded>
-        3 == 3
+        2 == 2
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE_THROWS" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9986,7 +9994,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_2 + 1
       </Original>
       <Expanded>
-        3 == 3
+        2 == 2
       </Expanded>
     </Expression>
     <OverallResult success="true" skips="0"/>
@@ -23237,6 +23245,6 @@ Approx( -1.95996398454005449 )
     </Section>
     <OverallResult success="true" skips="0"/>
   </TestCase>
-  <OverallResults successes="2198" failures="158" expectedFailures="43" skips="12"/>
+  <OverallResults successes="2199" failures="158" expectedFailures="43" skips="12"/>
   <OverallResultsCases successes="329" failures="96" expectedFailures="18" skips="6"/>
 </Catch2TestRun>
diff --git a/tests/SelfTest/Baselines/xml.sw.multi.approved.txt b/tests/SelfTest/Baselines/xml.sw.multi.approved.txt
index 91ac5a60..5b993e9b 100644
--- a/tests/SelfTest/Baselines/xml.sw.multi.approved.txt
+++ b/tests/SelfTest/Baselines/xml.sw.multi.approved.txt
@@ -9927,6 +9927,14 @@ Approx( 1.21999999999999997 )
   <TestCase name="MapGenerator can be skipped forward efficiently" tags="[generators][map]" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
       <Original>
+        map_calls == 0
+      </Original>
+      <Expanded>
+        0 == 0
+      </Expanded>
+    </Expression>
+    <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
+      <Original>
         map_generator.get() == 4
       </Original>
       <Expanded>
@@ -9938,7 +9946,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_1 + 1
       </Original>
       <Expanded>
-        2 == 2
+        1 == 1
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9954,7 +9962,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_1 + 1
       </Original>
       <Expanded>
-        2 == 2
+        1 == 1
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9970,7 +9978,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_2 + 1
       </Original>
       <Expanded>
-        3 == 3
+        2 == 2
       </Expanded>
     </Expression>
     <Expression success="true" type="REQUIRE_THROWS" filename="tests/<exe-name>/IntrospectiveTests/GeneratorsImpl.tests.cpp" >
@@ -9986,7 +9994,7 @@ Approx( 1.21999999999999997 )
         map_calls == map_calls_2 + 1
       </Original>
       <Expanded>
-        3 == 3
+        2 == 2
       </Expanded>
     </Expression>
     <OverallResult success="true" skips="0"/>
@@ -23236,6 +23244,6 @@ Approx( -1.95996398454005449 )
     </Section>
     <OverallResult success="true" skips="0"/>
   </TestCase>
-  <OverallResults successes="2198" failures="158" expectedFailures="43" skips="12"/>
+  <OverallResults successes="2199" failures="158" expectedFailures="43" skips="12"/>
   <OverallResultsCases successes="329" failures="96" expectedFailures="18" skips="6"/>
 </Catch2TestRun>
diff --git a/tests/SelfTest/IntrospectiveTests/GeneratorsImpl.tests.cpp b/tests/SelfTest/IntrospectiveTests/GeneratorsImpl.tests.cpp
index c415686b..297c67a9 100644
--- a/tests/SelfTest/IntrospectiveTests/GeneratorsImpl.tests.cpp
+++ b/tests/SelfTest/IntrospectiveTests/GeneratorsImpl.tests.cpp
@@ -709,6 +709,7 @@ TEST_CASE("MapGenerator can be skipped forward efficiently",
     };
 
     MapGenerator<int, int, decltype(map_func)> map_generator( map_func, values( { 0, 1, 2, 3, 4, 5, 6 } ) );
+    REQUIRE( map_calls == 0 );
     const int map_calls_1 = map_calls;
 
     map_generator.skipToNthElement( 4 );