test(context): Introduce an explicit value merging test

Introduces a test which will merge variables defined at every possible
layer together and ensure that the loaded context configuration is as
expected.

The test data provides an actual resource set template that can be
tested locally from a kontemplate source checkout:

    kontemplate template context/testdata/merging/context.yaml --var cliVar=cliVar

5 files changed, 51 insertions, 0 deletions

diff --git a/context/context_test.go b/context/context_test.go
index e700cf41978a..34c77cc9b7c6 100644
--- a/context/context_test.go
+++ b/context/context_test.go
@@ -293,3 +293,25 @@ func TestSetInvalidVariablesFromArguments(t *testing.T) {
 		t.Error("Expected invalid variable to return an error")
 	}
 }
+
+// This test ensures that variables are merged in the correct order.
+// Please consult the test data in `testdata/merging`.
+func TestValueMergePrecedence(t *testing.T) {
+	cliVars:= []string{"cliVar=cliVar"}
+	ctx, _ := LoadContext("testdata/merging/context.yaml", &cliVars)
+
+	expected := map[string]interface{}{
+		"defaultVar": "defaultVar",
+		"importVar": "importVar",
+		"globalVar": "globalVar",
+		"includeVar": "includeVar",
+		"cliVar": "cliVar",
+	}
+
+	result := ctx.ResourceSets[0].Values
+
+	if !reflect.DeepEqual(expected, result) {
+		t.Errorf("Merged values did not match expected result: \n%v", result)
+		t.Fail()
+	}
+}
diff --git a/context/testdata/merging/context.yaml b/context/testdata/merging/context.yaml
new file mode 100644
index 000000000000..df30d3d8cbe3
--- /dev/null
+++ b/context/testdata/merging/context.yaml
@@ -0,0 +1,15 @@
+# This context file is intended to test the merge hierarchy of
+# variables defined at different levels.
+---
+context: merging.in.kontemplate.works
+global:
+  globalVar: globalVar
+  includeVar: should be overridden (global)
+  cliVar: should be overridden (global)
+import:
+  - import-vars.yaml
+include:
+  - name: resource
+    values:
+      includeVar: includeVar
+      cliVar: should be overridden (include)
diff --git a/context/testdata/merging/import-vars.yaml b/context/testdata/merging/import-vars.yaml
new file mode 100644
index 000000000000..2a51352571a6
--- /dev/null
+++ b/context/testdata/merging/import-vars.yaml
@@ -0,0 +1,4 @@
+importVar: importVar
+globalVar: should be overridden (import)
+includeVar: should be overridden (import)
+cliVar: should be overridden (import)
diff --git a/context/testdata/merging/resource/default.yaml b/context/testdata/merging/resource/default.yaml
new file mode 100644
index 000000000000..040a19aaba25
--- /dev/null
+++ b/context/testdata/merging/resource/default.yaml
@@ -0,0 +1,5 @@
+defaultVar: defaultVar
+importVar: should be overridden (default)
+globalVar: should be overridden (default)
+includeVar: should be overridden (default)
+cliVar: should be overridden (default)
diff --git a/context/testdata/merging/resource/output.yaml b/context/testdata/merging/resource/output.yaml
new file mode 100644
index 000000000000..5920b2720780
--- /dev/null
+++ b/context/testdata/merging/resource/output.yaml
@@ -0,0 +1,5 @@
+defaultVar: {{ .defaultVar }}
+importVar: {{ .importVar }}
+globalVar: {{ .globalVar }}
+includeVar: {{ .includeVar }}
+cliVar: {{ .cliVar }}