improve wording of error message

internal/command/test_test.go

@@ -272,8 +272,7 @@ func TestTest_Runs(t *testing.T) {
 		},
 		"ephemeral_resource": {
 			expectedOut: []string{"0 passed, 1 failed."},
-			// TODO: Improve error message, say something about ephemeral resources not being accessible in tests due to their ephemeral nature
-			expectedErr: []string{"Ephemeral resource instance has expired", "Ephemeral resources not supported in the context of tests"},
+			expectedErr: []string{"Ephemeral resource instance has expired", "Ephemeral resources cannot be asserted"},
 			code:        1,
 		},
 	}

internal/moduletest/eval_context.go

@@ -211,8 +211,8 @@ func diagsForEphemeralResources(refs []*addrs.Reference) (diags tfdiags.Diagnost
 			if v.Resource.Mode == addrs.EphemeralResourceMode {
 				diags = diags.Append(&hcl.Diagnostic{
 					Severity: hcl.DiagError,
-					Summary:  "Ephemeral resources not supported in the context of tests",
-					Detail:   "Ephemeral resources are not supported in the context of terraform test.",
+					Summary:  "Ephemeral resources cannot be asserted",
+					Detail:   "Ephemeral resources are closed when the test is finished, and are not available within the test context for assertions.",
 					Subject:  ref.SourceRange.ToHCL().Ptr(),
 				})
 			}